Balloon catheters for angioplasty and other tissue expansion procedures are of course well known and in common clinical use. It is also known to provide angioplasty catheters which have a pair or more of balloons, one positioned inside the other, to permit the balloon assembly to be expanded to different, predetermined diameters by selective pressurization of the respective balloons through separate lumens. See for example Jang U.S. Pat. No. 4,744,366; Sahota U.S. Pat. No. 4,983,167; and Fogarty U.S. Pat. No. 4,338,942.
Multiple balloon catheters of the prior art require multiple inflation lumens, where the balloons are fluid impermeable, to permit the separate, independent inflation control of the respective balloons. However, the necessity for multiple inflation lumens requires that the diameter of the balloon catheter shaft must be larger than it otherwise would have to be, to accommodate such multiple inflation lumens.
In accordance with this invention, a balloon catheter for angioplasty or the like is provided in which multiple balloons are carried, one inside the other, on a catheter, being both controlled by a single inflation lumen even though the balloons are impermeable to the inflation medium. Nevertheless, the balloons may be inflated to differing diameters to provide an improvement in the versatility of use, which is so desired in angioplasty catheters and the like. This is coupled with a small diameter for the catheter shaft, since only one inflation lumen is required for two or more balloons.
Additionally, the balloon catheter of this invention can exhibit an expansion of a first, inner balloon at a first pressure/expansion gradient which exhibits a lesser amount of expansion per unit increase of pressure. Then, when the second balloon is expanded by itself, apart from the first balloon, to a greater diameter beyond the maximum expansion of the first balloon, it can typically expand at a second pressure/expansion gradient which has a greater amount of expansion per unit increase of pressure than the first pressure/expansion gradient. This is believed to provide a clinical advantage in the field of angioplasty, in that the first pressure/expansion gradient may be of a particularly desirable range to crack a hard stenosis in an artery as the inner balloon expands. Then, the second pressure/expansion gradient is more favorable for the expansion of the stenosis after it has been broken, and the initial resistance has been overcome by the expanding balloon. Also by this invention, the same catheter may provide differing balloon maximum inflation diameters for greater versatility.